1. Field of the Invention
The present invention relates to a color liquid crystal display panel and a manufacturing method of the same, and more particularly to a color liquid crystal display panel (hereinafter, referred to as CF-on-TFT panel) fabricated by forming a black matrix and a color filter on a TFT (Thin Film Transistor) substrate of the color liquid crystal panel made of a transparent insulating substrate having formed thereon a plurality of thin film transistors using amorphous silicon and a manufacturing method of the same. The present invention also relates to a liquid crystal display employing the CF-on-TFT panel as a color liquid crystal display panel.
2. Description of the Related Art
FIG. 1 is a cross section of a conventional liquid crystal display panel. As shown in the drawing, the conventional liquid crystal display panel is fabricated by laminating (1) a first substrate 1 (hereinafter, also referred to as TFT substrate) having switching elements such as TFTs (Thin Film Transistors) each composed of a gate electrode 2, a gate insulating film 4, a semiconductor layer 5, a source electrode 6, and a drain electrode 7, a wiring layer (not shown) for each of the electrodes 2, 6, and 7, a pixel electrode 12 in each pixel provided in a one-to-one correspondence to the TFT, a passivation film 8 covering all the foregoing components, an alignment film 18a, and a terminal 3 used as an electrical connection to an external circuit, and (2) a second substrate 16 having a black matrix 9, color filters 11R, 11G(not shown), and 11B respectively for three colors of R(Red), G(Green), and B(Blue), a transparent common electrode 17 such as ITO (Indium Tin Oxide), and an alignment film 18b to each other through a sealing material 19 applied at the circumference portion of the substrates 1 and 16, thereby assembling a panel with their respective film forming surfaces opposing each other and spherical spacers 20 being provided in between to maintain the gap between the substrates 1 and 16 at a constant distance, and filling a liquid crystal material 21 in the panel after baking the seal.
Known as a liquid crystal filling method for the liquid crystal material 21 are two-holes method and vacuum filling method. The former method comprises the steps of providing two holes through the panel at predetermined positions, and filling a liquid crystal material 21 in through one of the holes while evacuating the panel through the other, so that the liquid crystal material 21 is drawn into the panel. The latter method comprises the steps of providing an empty panel with one filling port, placing the liquid crystal material 21 in a vacuum (1xc3x9710xe2x88x922 to 1xc3x9710xe2x88x924 Torr) to allow the liquid crystal material 21 to adhere to the filling port, and subsequently restoring the pressure gradually to atmospheric pressure, so that the liquid crystal material 21 is filled in the panel by a pressure difference between the interior and exterior of the liquid crystal panel. Presently, the latter method is used in most of the cases.
Next, after the liquid crystal is filled, the filling port is sealed. Then, polarizing plates 24a and 24b are laminated to the outside surfaces of the substrates 1 and 16, respectively, whereby a liquid crystal panel is completed, which can be irradiated by light emitted from the back light through the first substrate 1 and second substrate 16.
In order to achieve high definition, the liquid crystal panel of this type has to increase the density of the pixels. However, because the conventional liquid crystal panel having the color filter 11 and black matrix 9 formed on the counter substrate causes an error in the position alignment during the fabrication procedure, allowance has to be made, which makes it difficult to secure the area (numerical aperture) of the pixel opening as large as possible.
In contrast, a method of forming the color filter and black matrix on the active matrix substrate having thereon formed the switching elements such as TFTs, that is, a so-called CF(Color Filter)-on-TFT, is proposed in Japanese Patent Laid-open Publication Nos. Hei 8-122824 and 9-292633.
In either case of these publications, because the color filter and black matrix are formed on the CF-on-TFT substrate, no allowance is necessary for the position alignment, thereby simplifying the manufacturing procedure while increasing the numerical aperture of the pixel.
With the panel of the CF-on-TFT structure, however, reflection of external light is greater than the conventional liquid crystal display panel, and therefore, there occurs a problem that the display quality deteriorates under bright external light circumstances.
FIGS. 2A and 2B are explanatory views showing external light reflection mechanisms of liquid crystal display panels. The above problem will be explained with reference to FIGS. 2A and 2B. Because ITO has the larger refractive index (n) (n=approx. 2.0) than those of the alignment films 18a and 18b (n=approx. 1.6) and glass substrate (n=approx. 1.4), the reflected components of external light are mainly the reflection from the ITO on the counter substrate and the reflection from the ITO of the pixel electrode 12.
Also, reflection from the scanning lines or signal lines is noticeable. As shown in FIG. 2A, because reflected light passes through the RGB color filter 11 twice in the conventional TFT and CF separation type liquid crystal display panel, reflected light attenuates in a satisfactory manner. On the contrary, as shown in FIG. 2B, reflected light does not attenuate with the color filter 11 in the liquid crystal display panel of the CF-on-TFT structure, and a quantity of reflected light is greater than that of reflected light from the conventional panel.
In particular, the panel of the CF-on-TFT structure has a problem that reflected light of green light having the wavelength xcex=550 nm or so is especially noticeable under bright external light circumstances.
Incidentally, a reflection preventing film is generally provided to reduce the reflection, and Japanese Patent Laid-open Publication Nos. 6-214252 and 10-154817 disclose a technique to take out reflected light effectively by providing the reflection preventing film over and beneath the counter electrode ITO, so that reflection efficiency of the liquid crystal light bulb of the reflecting type is increased.
In this case, however, the reflection preventing film is used to take out the reflected light effectively, and for this reason, dependency on the location of the reflected light, namely the display image, becomes so great that high-quality display performance cannot be achieved unless the refractive index and film thickness of the reflection preventing film are controlled accurately. Therefore, the reflection preventing film has to be made of an inorganic material by means of sputtering or the like, which poses a problem that an additional step is added to the manufacturing procedure of the liquid crystal display.
As has been discussed and shown in FIG. 2B, with the liquid crystal display panel of the CF-on-TFT structure having the color filter 11 formed on the TFT substrate, reflection of external light from ITO on the counter substrate and the ITO of the pixel electrode 12, or reflection from the signal lines and scanning lines is noticeable in comparison with the conventional TFT and CF separation type liquid crystal display panel shown in FIG. 2A, and in order to meet recent demand of high-quality image of the high density structure, deterioration of the image quality caused by the reflection particularly from the scanning lines and signal lines has to be prevented.
Further, in providing the reflection preventing film over and beneath ITO to prevent the deterioration of the image quality, a film of an inorganic material having predetermined refractive index and film thickness has to be formed by means of sputtering or the like, which results in a problem that an additional step is added to the manufacturing procedure of the liquid crystal display panel.
It is therefore an object of the present invention to provide a panel of the CF-on-TFT structure having an excellent display quality with less reflection of external light, and a manufacturing method of the same as well as a liquid crystal display.
A color liquid crystal display panel of the present invention includes: a first substrate; pixel electrodes, formed on the first substrate, for forming individual pixels; thin film transistors, formed on the first substrate, for functioning as switching elements for the individual pixels; a passivation film formed to cover the thin film transistors; a black matrix and a color filter formed over the passivation film; an overcoat layer formed to cover the black matrix and color filter; a second substrate provided to oppose the first substrate; a transparent common electrode formed on the second substrate; a sealing material for laminating the first substrate and second substrate at their respective frame portions; a liquid crystal material filled in a space between the first substrate and second substrate; and a mechanism or a member for shifting a wavelength of reflected light of incident light to a shorter wavelength side.
It is preferable that the shifting mechanism or shifting member sets retardation of a space distance sandwiched between the first substrate and second substrate and refractive index anisotropy of the liquid crystal material filled in the space closer to blue.
Also, an in-plane spacer may be used to maintain the space distance sandwiched between the first substrate and second substrate.
Further, a transparent resist film may be used at an in-plane to maintain the space distance sandwiched between the first substrate and second substrate.
Furthermore, an accumulation portion of the color filter may be formed at an in-plane to maintain the space distance sandwiched between the first substrate and second substrate.
In addition, for example, a fluorine liquid crystal mixture is used as the liquid crystal material filled in the space sandwiched between the first substrate and second substrate.
Also, the transparent resist film formed at the in-plane may be formed on the first substrate.
Moreover, the accumulation portion of the color filter formed at the in-plane is formed on the first substrate, for example.
A manufacturing method of a color liquid crystal display panel of the present invention comprises the steps of: forming a plurality of thin film transistors and a wiring layer on a first substrate; forming a passivation film entirely over the first substrate to cover the thin film transistors and wiring layer; forming a black matrix at least over a semiconductor layer in the thin film transistors and a frame at a circumference portion of the substrate; forming a color filter layer; forming an overcoat layer entirely over the first substrate to cover the black matrix and color filter layer; forming a pixel electrode by providing a contact through hole to the overcoat layer; providing a sealing material at a circumference portion on a thin film transistor surface of the first substrate; laminating a second substrate provided with a transparent common electrode to the first substrate with the sealing material in such a manner that the transparent common electrode opposes the thin film transistor surface of the first substrate; and filling a liquid crystal material in a space between the laminated substrates.
In this case, it is preferable that retardation of a space distance sandwiched between the first substrate and second substrate and refractive index anisotropy of the liquid crystal material filled in the space is set closer to blue.
Also, for example, in-plane spacers are scattered in the space between the first substrate and second substrate to maintain the space distance sandwiched between the first substrate and second substrate.
Further, a transparent resist film may be formed at an in-plane on the first substrate by means of photolithography to maintain the space distance sandwiched between the first substrate and second substrate.
Furthermore, an accumulation portion of the color filter layer may be formed at an in-plane on the first substrate by means of photolithography, printing, or electro-deposition to maintain the space distance sandwiched between the first substrate and second substrate.
Also, a fluorine liquid crystal mixture may be used as the liquid crystal material filled in the space sandwiched between the first substrate and second substrate.
According to the color liquid crystal display panel and the manufacturing method of the same, in a color liquid crystal display panel of a CF-on-TFT structure having a black matrix and a color filter formed on a TFT substrate, reflected light of external light from a pixel electrode ITO can be reduced by selecting and controlling a gap (d) of the CF-on-TFT panel and refractive index anisotropy (xcex94d) of a liquid crystal material by exploiting the presence of wavelength dependency between retardation (xcex94nd) and light transmittance. Consequently, a liquid crystal display of a CF-on-TFT structure with less reflection can be provided without providing a reflection preventing film.
A liquid crystal display of the present invention displays an image by using the foregoing color liquid crystal display panel.
Also, another liquid crystal display of the present invention displays an image by using the color liquid crystal display panel manufactured by the foregoing manufacturing method of a color liquid crystal display panel.
The nature, principle, and utility of the invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.